Clinical significance of 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography for the assessment of 131I-metaiodobenzylguanidine therapy in malignant phaeochromocytoma

The aim of this study was to evaluate the significance of 2-[F-18]fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) in the assessment of the therapeutic response to I-131-metaiodobenzylguanidine (MIBG) in malignant phaeochromocytoma. We reviewed the records of 11 patients (7 men and 4 women) with malignant phaeochromocytoma who underwent I-131-MIBG therapy (100-200 mCi). F-18-FDG PET and serum catecholamine assays were performed 3 months before and after the first dose of I-131-MIBG. FDG uptake was evaluated in the observed lesions using the maximum standardised uptake value (SUVmax). The average SUVmax of all lesions (ASUV) was calculated. If more than five lesions were identified, the average SUVmax of the five highest SUVmax (ASUV5) was calculated. The ratio of pre- and post-therapy values was calculated for the highest SUVmax (rMSUV), ASUV (rASUV), ASUV5 (rASUV5), CT diameter (rCT) and serum catecholamine (rCA). Responder (R) and non-responder (NR) groups were defined after a clinical follow-up of at least 6 months according to changes in symptoms, CT, magnetic resonance imaging (MRI) and I-123-MIBG scan. Post-therapy evaluation revealed five R and six NR patients. The size of the target lesions was not significantly different before and after therapy (p > 0.05). However, ASUV and ASUV5 were significantly lower in the R group (rASUV 0.64 +/- 0.18, rASUV5 0.68 +/- 0.17) compared to the NR group (rASUV 1.40 +/- 0.54, rASUV5 1.37 +/- 0.61) (p < 0.05). F-18-FDG PET can be potentially used to evaluate the response of malignant phaeochromocytoma to I-131-MIBG therapy.